Proximity sensor system having a proximity sensor with a bipolar signal output

ABSTRACT

The present invention relates to a proximity sensor system comprising a sensor generating two types of pulse signals having opposite polarities in order to detect two different, small, metallic objects and to distinguish the objects. The proximity sensor system can involve at least two metallic objects to be detected having different magnetic properties; a sensor comprising a magnetic core having a plurality of legs and a toroidal coil winding fitted and supported onto at least one of the legs of the magnetic core; and an electronic circuit processing output signals from the sensor. The sensor generates predetermined signals having opposite polarities when metallic objects pass in proximity to the sensor. Suitable metallic objects include those made of ferromagnetic metal and diamagnetic or paramagnetic metal. The sensor generates a positive pulse signal when the ferromagnetic metallic object passes by the sensor, and the sensor generates a negative pulse signal when the diamagnetic or paramagnetic metallic object passes by the sensor.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application hereby claims priority to international patentapplication No. PCT/KR01/00326 having an international filing date ofMar. 3, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sensor, and more particularly to asensor system having a proximity sensor utilizing magnetic properties ofmetals.

2. Description of the Related Art

A proximity sensor detects an object when the object approaches withinthe detection boundary of the sensor. Detecting metallic objects isparticularly useful in such applications as automation for assemblylines in a factory. In many instances, magnetic properties of metals areutilized as a principle for detection. There are many varieties ofproximity sensors that utilize magnetic properties of metals.

In most proximity sensor applications, the objects to be detected aremuch larger than the proximity sensor, and the objects are easilydetected because their magnetic couplings are strong. When the objectsto be detected are small compared with the dimensions of the sensor,e.g. in a range of a few millimeters, the magnetic couplings are weak,and the detection of such objects is difficult. One application fordetecting small objects is counting small teeth on a rapidly rotatinggear in order to monitor the uniformity of the rotational speed of thegear. In such an application, special techniques need to be implementedsuch as making the sensors very small and limiting the detectionboundaries of the sensors to be very short. In certain otherapplications, it may be necessary for one sensor to distinguish theobjects as well as detect proximity. When the relative positions of twoseparate objects are critically important information, the capability ofperforming two functions with one sensor is advantageous and much moreconvenient.

SUMMARY OF THE INVENTION

The object of the invention is to provide a proximity sensor systemcomprising a sensor generating two types of pulse signals havingopposite polarities in order to detect two different small, metallicobjects and distinguish the objects.

Another object of the invention is to provide a proximity sensor systemfor measurement of torque output from an automobile clutch-disc.

The invention describes a technique by which two different metallicobjects, for example a ferromagnetic object and a diamagnetic object,are separately and simultaneously detected by one sensor. The sensor ofthe present invention generates two signals having different polaritiesfor two magnetically different metallic objects so that the sensor candistinguish the different metallic objects.

According to one aspect of the invention, there is provided a proximitysensor system comprising at least two metallic objects to be detectedhaving different magnetic properties from each other, a sensorcomprising a magnetic core having a plurality of legs and a toroidalcoil winding being fitted and supported onto at least one of the legs ofthe magnetic core, and an electronic circuit processing output signalsfrom the sensor. The sensor generates predetermined signals havingopposite polarities when the metallic objects pass by in proximity tothe sensor.

Preferably, the metallic objects include a metallic object made offerromagnetic metal and a metallic object made of diamagnetic orparamagnetic metal.

Preferably, the sensor generates a positive pulse signal when theferromagnetic metallic object passes by the sensor, and the sensorgenerates a negative pulse signal when the diamagnetic or paramagneticmetallic object passes by the sensor.

Preferably, the electronic circuit further comprises an oscillator toprovide the sensor with an alternating current, and comprises ahalf-wave rectifier to process output signals from the sensor, alow-pass filter and an amplifier.

According to another aspect of the invention, there is provided aproximity sensor system for a device for real time measurement of torqueoutput from an engine to a transmission of an automobile comprising aplate type clutch with a clutch plate, a clutch shaft for connecting theclutch plate to a transmission, and an axle guide tube for surroundingthe clutch shaft over a length of the clutch shaft. The clutch platecomprises an intermediate body member with a hub attached at a centralportion thereof, and low and upper body members being adapted to bepositioned onto lower and upper surfaces of the intermediate body memberrespectively. The lower and upper body members are formed with centralapertures penetrated by the hub and are circumferentially displaceablerelative to the intermediate body member by a damper spring means. Theproximity sensor system comprises a first plurality of axially extendingposts formed equidistantly around a periphery of upper portion of thehub and made of a metal having a predetermined magnetic property, asecond plurality of axially extending posts formed equidistantly arounda circumference of the central aperture of the upper body member andmade of a metal having a magnetic property different from the firstposts, a sensor comprising a magnetic core having a plurality of legsand a toroidal coil winding, fitted and supported onto at least one ofthe legs of the magnetic core, and an electronic circuit processingoutput signals from the sensor. The second posts are disposed radiallyoutside the first posts. The sensor is positioned radially inside thefirst and second posts, and disposed onto the tip portion of the axleguide tube to face the first and second posts. The sensor generatespredetermined signals having different polarities when the first andsecond posts pass by the sensor respectively.

DESCRIPTION OF THE FIGURES

FIGS. 1(a) and 1(b) are elevated perspective views showing non-assembledand assembled states of a sensor according to the present invention,respectively.

FIG. 2 is a schematic view showing magnetic flux from a sensor, whereinFIG. 2(a) is a view showing a state with no objects to be detected, FIG.2(b) is a view showing detection of a ferromagnetic object, and FIG.2(c) is a view showing detection of a diamagnetic object.

FIG. 3 is a block diagram of an electronic circuit used in a system ofthe present invention.

FIG. 4 shows modulated carrier signals.

FIG. 5 shows demodulated pulse signals.

FIG. 6 shows an example of the proximity sensor system according to thepresent invention applied to a clutch-disc torque measurement sensorsystem for an automobile.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is embodied as a proximity sensor system, whereina proximity sensor operates in conjunction with specific objects to bedetected and generates pulses when the objects pass by in proximity tothe sensor. The proximity sensor system of the invention has at leastthree aspects, a sensor, objects to be detected and an electroniccircuit.

As shown in FIGS. 1(a) and (b), a sensor 1 includes a magnetic core 11and a toroidal coil winding 12. The magnetic core 11 can be made in theshape of an “E” or in the shape of a two-leg “⊂,” and the coil winding12 is supported by fitting a central portion thereof onto at least oneprotruding leg of the magnetic core 11. In the embodiment shown in FIGS.1(a) and 1(b), the magnetic core 11 is made in the shape of an “E,” andthe coil winding 12 is supported by fitting a central portion thereofonto the center-leg of the three protruding legs.

When an alternating current passes the coil winding 12, the sensor 1produces a magnetic flux as represented in FIG. 2(a). When aferromagnetic object 21 approaches the vicinity of the sensor, themagnetic flux is strengthened as shown in FIG. 2(b). However, if adiamagnetic object 22 approaches the vicinity of the sensor, themagnetic flux is weakened as shown in FIG. 2(c).

Sensor 1 generates two types of pulse signals having opposite polaritiesdepending upon the properties of the objects to be detected, thusenabling the sensor system to distinguish two different types ofobjects. For example, if one of the two type objects is made offerromagnetic metal, such as iron, nickel or their alloys, and the otherobject is made of diamagnetic (or paramagnetic) metal, such as copper oraluminum, the sensor 1 generates a positive (+) pulse signal when aferromagnetic metallic object passes sensor 1, and it generates anegative (−) pulse signal when a diamagnetic (or paramagnetic) metallicobject passes sensor 1.

FIG. 3 shows a block diagram of an example for an electronic circuitused in the proximity sensor system of the present invention. Theelectronic circuit includes an oscillator to provide the sensor with analternating current, a half-wave rectifier to process output signalsfrom the sensor, a low-pass filter and an amplifier.

The alternating current that flows in the coil winding 12 of the sensor1 is supplied by the oscillator, which generates high frequencyalternating currents. The coil winding 12 acts as an inductive load tothe oscillator. When the objects to be detected approach the sensor, amagnetic flux is modified as shown in FIGS. 2(b) and 2(c), therebymodifying impedance of the inductive load so that output voltage signalsare modulated as shown in FIG. 4. The modulated carrier signals passthrough the half-wave rectifier and the low-pass filter to producedemodulated output pulse signals, as shown in FIG. 5.

According to the proximity sensor system of the present invention, thesensor generates pulse signals having different polarities depending onthe magnetic properties of the objects approaching the sensor, thusenabling the sensor system to provide two types of information with onesensor. One possible form of information is whether a certain typemetallic object is approaching the sensor, while the other is aboutanother type of metallic object approaching the sensor.

In the foregoing embodiment, it has been stated that the sensorgenerates a positive pulse signal for the ferromagnetic object, and anegative pulse signal for the diamagnetic (or paramagnetic) object.However, it should be noted that the polarities of the pulse signals areinterchangeable depending on processing of the signals in the electroniccircuit.

According to the construction of the sensor system of the presentinvention, as the sensor generates two pulse signals having differentpolarities depending upon the types of objects to be detected, theobjects can be easily detected and distinguished, thus improving thereliability of detecting and distinguishing the objects, even in thecase of small objects.

Although the proximity sensor system of the invention has been describedand illustrated for a specific embodiment, the invention is not intendedto be limited to the embodiment, and may be modified or varied withregard to construction, without departing from the spirit and principlesdisclosed in the claims below.

INDUSTRIAL APPLICABILITY

The proximity sensor system of the present invention can be applied tovarious fields, for example, a device for real time measurement oftorque from an automobile engine such disclosed in InternationalApplication Publication No. WO 99/58943.

In the device for real time measurement of torque from an automobileengine, a planar clutch plate that is a component of an automobileequipped with a manual transmission, can be slightly modified byincorporating two types of metallic posts having different magneticproperties corresponding to the metallic objects as described in thepresent invention. As shown in FIG. 6, one type of metallic posts 21 iswelded on a hub of the clutch plate, and the other type of metallicposts 22 is welded on the clutch plate. The sensor 1 is mounted ontomounding hole of a clutch axle guide tube (not shown in FIG. 6) placedradially inside the metallic posts. When the automobile is in motion,the clutch plate rotates, but the sensor mounted on the axle guide tuberemains stationary. Thus, the metallic posts pass-by in proximity of thesensor. The sensor detects the types of metallic posts and generatespulse signals having opposite polarities.

Through generated pulse signals having opposite polarities, the relativeangular displacements of the two types of posts 21, 22 during rotationof the clutch plate, can be easily detected and distinguished, thusimproving reliability and accuracy of real time measurement of torquefrom an engine.

1. A proximity sensor system comprising: a ferromagnetic metallic objectfor being detected; a diamagnetic metallic object for being detected; asensor for generating a positive pulse signal, said positive pulsesignal being generated when said ferromagnetic metallic object passes bysaid sensor, said sensor generating a negative pulse signal when saiddiamagnetic metallic object passes by said sensor, said sensor furthercomprising a magnetic core having a plurality of legs and a toroidalcoil being fitted and supported onto at least one of said plurality oflegs; and an electronic circuit for processing an output signal fromsaid sensor.
 2. The proximity sensor system of claim 1, wherein theproximity sensor system further comprises an oscillator for providingsaid sensor with an alternating current, and wherein said electroniccircuit comprises a half-wave rectifier for processing said outputsignal from said sensor, a low-pass filter, and an amplifier.
 3. Aproximity sensor system for real time measurement of torque from anengine to a transmission of an automobile having a plate type clutchwith a clutch plate, a clutch shaft for connecting the clutch plate tothe transmission, and an axle guide tube for surrounding a length of theclutch shaft, the clutch plate comprising: an intermediate body memberwith a hub being connected at a central portion thereof, a lower bodymember, and an upper body member positioned onto a lower surface and anupper surface of said intermediate body member respectively, said lowerbody member and said upper body member being formed with a plurality ofcentral apertures, said plurality of central apertures being penetratedby said hub and being circumferentially displaceable relative to saidintermediate body member by a damper spring means, the proximity sensorsystem comprising: a first plurality of axially extended posts beingmade of a ferromagnetic metal, said first plurality of axially extendedposts being formed equidistantly around a periphery of an upper portionof said hub; a second plurality of axially extended posts being made ofa diamagnetic metal, said second plurality of axially extended postsbeing formed equidistantly around a circumference of at least one ofsaid plurality of central apertures of said upper body member; a sensorfor generating a positive pulse signal when said first plurality ofaxially extended posts passes by said sensor, wherein said sensorgenerates a negative pulse signal when said second plurality of axiallyextended posts passes by said sensor, said sensor having a magnetic corehaving a plurality of legs and a toroidal coil windingly fitted andsupported onto at least one of said plurality of legs, said sensor beingpositioned radially in said first plurality of axially extended posts,and said second plurality of axially extended posts and being disposedonto a tip portion of an axle guide tube to face said first plurality ofaxially extended posts and said second plurality of axially extendedposts; and an electronic circuit for processing an output signal fromsaid sensor.
 4. A proximity sensor system comprising: a ferromagneticmetallic object for being detected; a paramagnetic metallic object forbeing detected; a sensor for generating a positive pulse signal whensaid ferromagnetic metallic object passes said sensor, said sensor forgenerating a negative pulse signal when said paramagnetic metallicobject passes said sensor, said sensor having a magnetic core with aplurality of legs and a toroidal coil windingly fitted and supportedonto at least one of said plurality of legs; and an electronic circuitfor processing output signals from said sensor.